Immunity to SARS-CoV-2, acquired through infection or immunization, is critical to stop the COVID-19 pandemic.

A study led by the University of Zurich (UZH) has now identified another factor that contributes to SARS-CoV-2 immunity — prior antibody responses to other, non-pathogenic coronaviruses.

“People who have had strong immune responses to other human coronaviruses also have some protection against SARS-CoV-2 infection,” said Alexandra Trkola.

The researchers employed a newly designed technique to determine antibody levels against four different human coronaviruses in 825 serum samples collected prior to the outbreak of SARS-CoV-2. Additionally, they evaluated 389 samples from donors who had been infected with SARS-CoV-2.

By combining these investigations with computer simulations, the team was able to anticipate precisely how efficiently the antibodies would bind to and kill invading viruses.

The researchers were able to establish that individuals infected with SARS-CoV-2 had lower levels of antibodies against coronaviruses that cause common colds than those who were not infected. Additionally, those with high antibody levels against harmless coronaviruses were less likely to have been hospitalized following infection with SARS-CoV-2.

“Our study shows that a strong antibody response to human coronaviruses increases the level of antibodies against SARS-CoV-2. So someone who has gained immunity to harmless coronaviruses is therefore also better protected against severe SARS-CoV-2 infections,” said Trkola.

This is referred to as cross-reactivity, and it also occurs with T cell responses, the immune system’s additional line of defense against pathogens.

Individuals are fully protected against SARS-CoV-2 infection only quickly after recovering from an infection or receiving an effective vaccine. This is when the virus’s antibody levels are still extremely high. As these levels decline over time, infection becomes inevitable, but the immunological memory swiftly reactivates the body’s defenses, including antibody synthesis and T cell defense.

“Of course, immune responses targeting SARS-CoV-2 that are mounted by the memory cells are far more effective than cross-reactive responses. But even though the protection isn’t absolute, cross-reactive immune responses shorten the infection and reduce its severity. And this is exactly what is also achieved through vaccination, just much, much more efficiently,” added Trkola.

It is unclear at this point whether this cross-reactivity occurs in the reverse way as well. Immunity against SARS-CoV-2 – obtained, for example, through vaccination – does not yet provide protection against other human coronaviruses.

“If SARS-CoV-2 immunity also offers some degree of protection from infection with other coronaviruses, we would be a significant step closer to achieving comprehensive protection against other coronaviruses, including any new variants,” the virologist explained.

This notion is also supported by the fact that cross-reactive protection is most likely reliant on T cells, rather than antibodies.

Source: 10.1038/s41467-021-27040-x

Image Credit: Getty

You were reading: The factor that offers extra protection from Covid-19